"There's a new level of cachet and luxury to be achieved. This is not the normal New Yorker's luxury," said Sofia Song, vice president of research for the real estate site StreetEasy.com. "This has nothing to do with market dynamics. It's about cachet."

At the turn of the 20th century, industrial billionaires such as Andrew Carnegie, John D. Rockefeller and Cornelius Vanderbilt lined Fifth Avenue (then known as Millionaire's Row) with megamansions. Today's crop of multimillion-dollar penthouse buyers are titans of industry, though many are from abroad, such as Russian billionaire Dmitry Rybolovlev, who broke records when he purchased a penthouse at 15 Central Park West for $88 million, the most that has ever been paid for a New York City apartment.

Real estate experts peg the beginning of the trophy apartment explosion to the opening of ultra-luxe 15 Central Park West in 2008. In 2005, before the foundation had even been completed, hedge fund manager Daniel Loeb bought an eight-bedroom penthouse for a then-record-breaking $45 million.

"A few decades ago, there were only a few mega apartments," said Faith Hope Consolo, a chairwoman at Prudential Douglas Elliman. "Now, there is so much demand, it is becoming more of the norm than the exception."